The study deals with the chemical mechanisms whereby arthropods interact with other organisms in their environment. Particular attention is being given to substances that serve for protection against predators or microorganisms, or for communication with mates or siblings. The substances are being studied from the chemical, biochemical, and ecological points of view, in hopes of clarifying both their basic and applied significance. BIBLIOGRAPHIC REFERENCES: Eisner, T., Kriston, I. and Aneshansley, D. 1976. Defensive behavior of a termite. Behav. Biol. Sociobiol. I. 83-125. Eisner, T. and Dean, J. 1976. Ploy and Counterploy in Predator-Prey Interactions: Orb-Weaving Spiders versus Bombardier Beetles. Proc. Nat. Acad. Sci. 73 (4): 1365-1367.